Works like a charm, thanks!! Again, I learned a lot.
My new test-file now includes audio for mono-invert, stereo-invert,
mono-half-left-invert, mono-half-right-invert:
https://cloud.4ohm.de/s/bsbAA4Jk3NBPLRD
I included cases for corr = -1 and corr between -1 and 0.
I also added volume compensation for corr = 1 and corr = -1.
And hey, it works! ;)
I would be happy if you find a minute to review. (and maybe improve) (or
comment on clumsiness) ;)
Comments / todo:
- On the way, I lost is fading between the cases. Probably doable with
smoo'ing all corr_ cases?
- I guess volume compensation could be improved by checking the panning
when corr = 1 or corr = -1. but for now I am happy.
Klaus
import("stdfaust.lib");
avg(t,x)= fi.pole(p,(1- p)* x)// 1-pole lowpass as average
with{
p= exp((((-2.0* ma.PI)/ t)/ ma.SR));
};
var(t,x)= avg(t,(x- avg(t,x))^ 2);// variance
sd(t,x)= sqrt(var(t,x));// standard deviation
cov(t,x1,x2)= avg(t,(x1- avg(t,x1))* (x2- avg(t,x2)));// covariance
corr(t,x1,x2)= cov(t,x1,x2)/ max(ma.ma.EPSILON,(sd(t,x1)* sd(t,x2)));//
correlation
t= .1;// averaging period in seconds
correlate_meter(x,y)= x,y<:x,attach(y,(corr(t):hbargraph("corr",-1,1))):_,_;
correlate_correct(t,l,r)= out_pos1,out_neg1,out_0,out_pos,out_neg:>_,_with{
th=.001;
corr_pos1= avg(t,(corr(t,l,r)>(1-th)));
corr_neg1= avg(t,corr(t,l,r)<(-1+th));
corr_0= avg(t,((corr(t,l,r)<th)& (corr(t,l,r)>(0-th))));
corr_pos= avg(t,((corr(t,l,r)>(0+th))& (corr(t,l,r)<(1-th))));
corr_neg= avg(t,((corr(t,l,r)>(-1+th))& (corr(t,l,r)<(0-th))));
out_pos1= ((l* corr_pos1+ r* corr_pos1)/2),((l* corr_pos1+ r* corr_pos1)/2);
out_neg1= ((l* corr_neg1+ (-r)* corr_neg1)/2),((l* corr_neg1+ (-r)*
corr_neg1)/2);
out_0= (l* corr_0+ r* corr_0),(l* corr_0+ r* corr_0);
out_pos= l* corr_pos,r* corr_pos;
out_neg= l* corr_neg,(0-(r* corr_neg));
};
process=
_,_:correlate_meter:ba.bypass2(hslider("bypass",0,0,1,1),correlate_correct(t));
On 09.08.21 18:26, Dario Sanfilippo wrote:
> Hi, Klaus.
>
> From the top of my head, maybe something like this:
>
> import("stdfaust.lib");
> avg(t, x) = fi.pole(p, (1 - p) * x) // 1-pole lowpass as average
> with {
> p = exp((((-2.0 * ma.PI) / t) / ma.SR));
> };
> var(t, x) = avg(t, (x - avg(t, x)) ^ 2); // variance
> sd(t, x) = sqrt(var(t, x)); // standard deviation
> cov(t, x1, x2) = avg(t, (x1 - avg(t, x1)) * (x2 - avg(t, x2))); //
> covariance
> corr(t, x1, x2) = cov(t, x1, x2) / max(ma.ma.EPSILON, (sd(t, x1) *
> sd(t, x2))); // correlation
> t = .1; // averaging period in seconds
> correlate_meter(x,y) = x,y <: x , attach(y, (corr(t) :
> hbargraph("corr",-1,1))) : _,_;
> correlate_correct(t,l,r) = (l + r) * mSmoo + l * stSmoo , (l + r) *
> mSmoo + r * stSmoo
> with {
> th = .001;
> isMono = (corr(t,l,r) > (1 - th)) | ((corr(t,l,r) < th) & ((avg(t, l *
> l) < th) | ((avg(t, r * r) < th))));
> mSmoo = avg(t, isMono);
> stSmoo = 1.0 - mSmoo;
> };
> process = _,_ : correlate_meter : correlate_correct(t);
>
> I think that several non-mono cases can result in a correlation that
> is close to zero so I'd add another condition to check if either of
> the two channels is really quiet.
>
> Ciao,
> Dr Dario Sanfilippo
> http://dariosanfilippo.com <http://dariosanfilippo.com>
>
>
> On Mon, 9 Aug 2021 at 09:44, Klaus Scheuermann <[email protected]
> <mailto:[email protected]>> wrote:
>
> Dear Julius, dear Dario,
>
> thanks - again !
>
> @Julius:
>
> ba.if(1>corr(t,l,r)>0,l,(l+r))
>
> was my clumsy way of saying 'if corr is smaller than 1 AND greater
> than 0'. Or if you turn it around 'if corr ==0 OR corr ==1'. What
> would be the most elegant way to do this in faust?
> You are right about the L == -R case... I did not look into
> out-of-phase cases yet. Probably then the condition should be 'if
> corr nears -1 OR 0 OR 1', right?
>
> @Dario, the code works very nicely and the smoothing sounds
> delicious ;)
> By explaining my clumsy ba.if statement, you will understand, that
> I'd like mono-left and mono-right (which result in corr=0) to be
> centered, too. If corr nears 0 or 1, the result should be in the
> center. Same question: how to do an elegant OR condition?
>
> Another thing I was thinking about is, if it makes more sense to
> convert the stereo signal to M-S and regulate the S channel for
> mono or stereo. But it's probably the same result as smoothing
> between l+r,l+r and l,r.
>
> Cheers,
> Klaus
>
> On 09.08.21 00:56, Dario Sanfilippo wrote:
>> Hi, Klaus; nice to hear from you, Julius. :)
>>
>> As Julius points out, I also think that you'd need less demanding
>> thresholds: even for identical channels, the average using a
>> one-pole lp will oscillate and it might not be reliable if
>> checking against the corner case.
>>
>> I'd go with something like this, but Julius also has a point
>> about phase-inverted mono signals. Also, you may want to
>> normalise when you sum L and R. It was necessary to guard against
>> division by 0 too. I've included a smoother to avoid clicks when
>> switching.
>>
>> I've tested that with your audio example and it's all mono
>> except mono-left, mono-right, and stereo. Is that correct?
>>
>> import("stdfaust.lib");
>> avg(t, x) = fi.pole(p, (1 - p) * x) // 1-pole lowpass as average
>> with {
>> p = exp((((-2.0 * ma.PI) / t) / ma.SR));
>> };
>> var(t, x) = avg(t, (x - avg(t, x)) ^ 2); // variance
>> sd(t, x) = sqrt(var(t, x)); // standard deviation
>> cov(t, x1, x2) = avg(t, (x1 - avg(t, x1)) * (x2 - avg(t, x2)));
>> // covariance
>> corr(t, x1, x2) = cov(t, x1, x2) / max(ma.ma.EPSILON, (sd(t, x1)
>> * sd(t, x2))); // correlation
>> t = .5; // averaging period in seconds
>> correlate_meter(x,y) = x,y <: x , attach(y, (corr(t) :
>> hbargraph("corr",-1,1))) : _,_;
>> correlate_correct(t,l,r) = (l + r) * mSmoo + l * stSmoo ,(l + r)
>> * mSmoo + r * stSmoo
>> with {
>> isMono = corr(t,l,r) > .999;
>> mSmoo = avg(.05, isMono);
>> stSmoo = 1.0 - mSmoo;
>> };
>> process = _,_ : correlate_meter : correlate_correct(t);
>>
>> Ciao,
>> Dr Dario Sanfilippo
>> http://dariosanfilippo.com <http://dariosanfilippo.com>
>>
>>
>> On Mon, 9 Aug 2021 at 00:25, Julius Smith <[email protected]
>> <mailto:[email protected]>> wrote:
>>
>> And of course I mean "cross-correlation coefficient"
>>
>> On Sun, Aug 8, 2021 at 3:22 PM Julius Smith
>> <[email protected] <mailto:[email protected]>> wrote:
>>
>> Hi Klaus,
>>
>> I am late to this (just read some of the thread with
>> interest), and I have a question: what do you mean by "1
>> > corr(t,l,r) > 0" ? It appears to be "parsed" left to
>> right, so that the 2nd ">" only sees "1>0" most (all?) of
>> the time, which is always true (1) of course (so no
>> "else" activated). Maybe you want something like
>> "abs(corr(t,l,r)) > 0.95" ? (i.e., 95% correlation
>> deemed to be "panned mono"). I'm taking the absolute
>> value because I assume you don't care if the left channel
>> is merely the negative of the right (unless that's an
>> accepted cheezy "stereoizer" of sorts).
>>
>> FYI, this is what we call a time-domain "normalized
>> cross-correlation" or "correlation coefficient"
>> measurement (official buzzwords)
>>
>> Cheers,
>> Julius
>>
>>
>> On Sun, Aug 8, 2021 at 10:07 AM Klaus Scheuermann
>> <[email protected] <mailto:[email protected]>> wrote:
>>
>> Dear Dario,
>>
>> cool, your corr function gives me the desired
>> results. At least when feeding it to a meter.
>>
>> Here is my test audio which contains vocals in
>> mono-mid, mono-left, mono-right, mono-half-left,
>> mono-half-right, stereo:
>> https://cloud.4ohm.de/s/y9oZzqFGyrZT5ej
>> <https://cloud.4ohm.de/s/y9oZzqFGyrZT5ej>
>>
>> For mono-mid, mono-half-left, mono-half-right it shows 1.
>> For mono-left, mono-right it shows 0.
>> For stereo it shows values between 0 and 1.
>>
>> I would like to detect mono signals that are not
>> exactly in the middle and put them there. Stereo
>> signals should be unchanged.
>>
>> My code is here, but for some reason it does not work
>> correctly. Especially when corr shows 0, ba.if does
>> not go to the else-path.
>>
>> import("stdfaust.lib");
>> avg(t,x)= fi.pole(p,(1- p)* x)// 1-pole lowpass as
>> average
>> with{
>> p= exp((((-2.0* ma.PI)/ t)/ ma.SR));
>> };
>> var(t,x)= avg(t,(x- avg(t,x))^ 2);// variance
>> sd(t,x)= sqrt(var(t,x));// standard deviation
>> cov(t,x1,x2)= avg(t,(x1- avg(t,x1))* (x2-
>> avg(t,x2)));// covariance
>> corr(t,x1,x2)= cov(t,x1,x2)/ (sd(t,x1)*
>> sd(t,x2)):_;// correlation
>> t= 0.5;// averaging period in seconds
>> correlate_meter(x,y)=
>> x,y<:x,attach(y,(corr(t):hbargraph("corr",-1,1))):_,_;
>> correlate_correct(t,l,r)=
>>
>> ba.if(1>corr(t,l,r)>0,l,(l+r)),ba.if(1>corr(t,l,r)>0,r,(l+r));
>> process= _,_:correlate_meter:correlate_correct(t);
>>
>> Am I doing the ba.if wrong?
>>
>> Thank s very much,
>> Klaus
>>
>>
>> On 04.08.21 18:25, Dario Sanfilippo wrote:
>>> I had implemented a few statistics function a while
>>> back, kindly taken from Wikipedia, and they seem to
>>> produce the expected values mentioned on the
>>> webpage. I hope that these can be useful.
>>>
>>> Ciao,
>>> Dr Dario Sanfilippo
>>> http://dariosanfilippo.com <http://dariosanfilippo.com/>
>>>
>>> import("stdfaust.lib");
>>> avg(t, x) = fi.pole(p, (1 - p) * x) // 1-pole
>>> lowpass as average
>>> with {
>>> p = exp((((-2.0 * ma.PI) / t) / ma.SR));
>>> };
>>> var(t, x) = avg(t, (x - avg(t, x)) ^ 2); // variance
>>> sd(t, x) = sqrt(var(t, x)); // standard deviation
>>> cov(t, x1, x2) = avg(t, (x1 - avg(t, x1)) * (x2 -
>>> avg(t, x2))); // covariance
>>> corr(t, x1, x2) = cov(t, x1, x2) / (sd(t, x1) *
>>> sd(t, x2)); // correlation
>>> ph0 = os.phasor(2.0 * ma.PI, 200);
>>> red = sin(ph0) + .35 * sin(ph0 * 3.0) + .91 *
>>> sin(ph0 * 5.0);
>>> blue = sin(ph0) + .5 * sin(ph0 * 3.0) - .5 * sin(ph0
>>> * 5.0);
>>> red1 = sin(ph0) + sin(ph0 * 3.0);
>>> blue1 = sin(ph0) - sin(ph0 * 3.0) / 3.0;
>>> t = 1.0; // averaging period in seconds
>>> process = (red , blue : corr(t)) , (red1 , blue1 :
>>> corr(t));
>>>
>>>
>>>
>>> On Wed, 4 Aug 2021 at 16:52, Klaus Scheuermann
>>> <[email protected] <mailto:[email protected]>> wrote:
>>>
>>> Thanks Giuseppe,
>>>
>>> I checked it out, but somehow it still does not
>>> give me the desired result...
>>> I did some more research and found this, which
>>> indicates that it can be done with arctan more
>>> easily.
>>>
>>>> The way this is done on phase (correlation)
>>>> meters in audio equipment is rather simple:
>>>>
>>>> Phase = arctan(L/R)
>>>>
>>>> With phase of 45 or 225 = 1, and phase of 135
>>>> and 315 (-45) is -1.
>>>>
>>>> Essentially, the Y Axis is the L, and the X
>>>> axis is the R. The phase is simply the polar
>>>> angle of the vector between the two.
>>>>
>>>> This type of meters will show 1 if the signal
>>>> is mono, and -1 if the left and right are
>>>> perfectly phase inverted.
>>>>
>>>> Notice however, that phase meters of this type
>>>> also account for the magnitude in the polar
>>>> coordinates. So:
>>>>
>>>> Magnitude = (L^2 + R^2)^1/2
>>>>
>>>> Thus the actual meter display is a normalised
>>>> version of:
>>>>
>>>> Correlation = Phase * Magnitude
>>>>
>>>> I'm not sure that satisfies your requirements,
>>>> but this answers the question in the subject.
>>>>
>>> So I transfered this to faust, but it still
>>> behaves weired...
>>>
>>> import("stdfaust.lib");
>>> phase(l,r)= (l/r):aa.arctan;
>>> magnitude(l,r)= (l^2+ r^2)^1/2;
>>> correlate(l,r)= phase(l,r)* magnitude(l,r);
>>> correlate_meter(x,y)=
>>> x,y<:x,attach(y,(correlate:hbargraph("corr",-1,1))):_,_;
>>> process= _,_:correlate_meter:_,_;
>>>
>>> Any ideas?
>>>
>>> Klaus
>>>
>>> On 03.08.21 14:48, Giuseppe Silvi wrote:
>>>> Hi Klaus,
>>>> The filters are necessary to obtain a -1 +1 range, I
>>>> think.
>>>>
>>>> import("stdfaust.lib");
>>>>
>>>> correlate(l,r) = l*l ,r*r , l*r : par(i,3,
>>>> si.smooth(0.9)) : sqrt, sqrt, _ : *,_ : /;
>>>> correlate_meter(x,y) = x,y <: x , attach(y, (correlate
>>>> : hbargraph("corr”,-1,1)));
>>>>
>>>> process = correlate_meter;
>>>>
>>>> Try playing with the si.smooth coefficient.
>>>>
>>>> best,
>>>> giuseppe
>>>>
>>>>> On 3 Aug 2021, at 14:09, Klaus Scheuermann
>>>>> <[email protected]> <mailto:[email protected]> wrote:
>>>>>
>>>>> Could it be something like this?
>>>>>
>>>>> (according to the 'correct' algorithm in
>>>>> https://www.beis.de/Elektronik/Correlation/CorrelationCorrectAndWrong.html
>>>>>
>>>>> <https://www.beis.de/Elektronik/Correlation/CorrelationCorrectAndWrong.html>
>>>>> )
>>>>> import("stdfaust.lib");
>>>>>
>>>>> correlate(l,r) = l*l ,r*r , l*r : sqrt, sqrt, _ : *,_
>>>>> : / :_;
>>>>> correlate_meter(x,y) = x,y <: x , attach(y,
>>>>> (correlate : hbargraph("corr",-1,1))) : _,_;
>>>>>
>>>>> process = _,_ : correlate_meter: _,_;
>>>>>
>>>>> I am not sure about the lowpass filters though. Maybe
>>>>> not needed in the digital domain?
>>>>>
>>>>> Also, my code only returns -1 or 1 while it should be
>>>>> returning a range of -1 and 1, right?
>>>>>> The correlation is either expressed in % from -100%
>>>>>> to +100% or as the correlation factor, which ranges from -1 to +1. Note
>>>>>> that due to the correlation algorithm the level of both signals does not
>>>>>> matter, i.e., it does not influence the measured result.
>>>>>>
>>>>>> When a mono source is used for a stereo signal both
>>>>>> stereo channels will be +100% correlated. When e.g. in a stereo signal
>>>>>> both channels contain completely different signals, e.g. left (and only
>>>>>> left) is the trumpet and right (and only right) is the guitar these
>>>>>> stereo channels will be 0% correlated. With a third instrument appearing
>>>>>> in both channels, the correlation will be somewhere between 0 and +100%.
>>>>>>
>>>>> Ideas?
>>>>> Danke :)
>>>>> Klaus
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> On 03.08.21 12:48, Klaus Scheuermann wrote:
>>>>>> Hello List,
>>>>>>
>>>>>> I just wondered, if anyone has implemented a stereo
>>>>>> audio correlation
>>>>>> meter/analyser in faust?
>>>>>>
>>>>>> If yes - great!
>>>>>> If no - I have another project :)
>>>>>>
>>>>>> Here is what I found about the algorithm(s):
>>>>>>
>>>>>>
>>>>>> https://www.beis.de/Elektronik/Correlation/CorrelationCorrectAndWrong.html
>>>>>>
>>>>>> <https://www.beis.de/Elektronik/Correlation/CorrelationCorrectAndWrong.html>
>>>>>>
>>>>>>
>>>>>> I never learned analog electronic schematics, but it
>>>>>> seems it should not
>>>>>> be extremely hard to transfer to faust.
>>>>>>
>>>>>> Cheers, Klaus
>>>>>>
>>>>>>
>>>>>>
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